In a drive train of a vehicle (an automotive vehicle), a power transmission system which performs a gear-shift through a gear-shift mechanism and a speed-reduction mechanism through which an output torque of a driving source such as an engine (internal combustion engine) and an motor (electrically driven motor) is gear-shifted and is transmitted to driving wheels. Since toothed gears are used in the gear-shift mechanism and the speed-reduction mechanism, vibrations and noise sounds due to backrushes of the toothed gears are sometime generated so that vehicle occupants including a vehicle driver give unpleasant feelings.
For example, when positive-or-negative inversion occurs in the driving torque acted upon a driving shaft (driving wheels), vibrations, noises, and shocks are, accordingly, often introduced due to backlashes of the toothed gears.
In a Patent Document 1 discloses a technique to suppress the generation of the above-described shocks in association with the positive-or-negative inversion of this driving torque and to suppress a reduction in an energy efficiency. This technique estimates the driving torque acted upon the driving wheels when a brake is activated during a traveling of the vehicle and limits the output torque of the motor by a motor target braking torque of a variation rate smaller than a prescribed ordinary rate.